A central objective in ATM networks is to provide virtual circuits that offer consistent performance in the presence of stochastically varying loads on the network. This objective can be achieved in principle, by requiring that users specify traffic characteristics when a virtual circuit is established, so that the network can select a route that is compatible with the specified traffic and allocate resources as needed. While this does introduce the possibility that a particular virtual circuit will be blocked or delayed, it allows established virtual circuits to receive consistent performance as long as they remain active.
Ideally, a bandwidth management and congestion control mechanism should satisfy several competing objectives. First, it should provide consistent performance to those applications that require it, regardless of the other virtual circuits with which a given virtual circuit may be multiplexed. Second, it should allow high network throughputs even in the presence of bursty traffic streams. (For typical transfer applications, a single burst may be tens or hundreds of kilobytes long; that is, there may be more than 1000 ATM cells in a burst, while the buffers in the switching systems will typically contain room for only a few hundreds of cells.) Third, the specification of traffic characteristics should be simple enough that users can develop an intuitive understanding of the specifications and flexible enough that inaccurate specifications don't have seriously negative effects on the user. Fourth, it should not artificially constrain the characteristics of user traffic streams; the need for flexibility in ATM networks makes it highly desirable that traffic streams be characterized parametrically, rather than by attempting to fit them into a pre-defined set of traffic classes. Fifth, it must admit a simple realization for reasons of economy and reliability. Less crucial, but in our view, also important, is the requirement that the bandwidth management mechanism accommodate multicast virtual circuits with multiple transmitters. All proposals we have seen for connection management in ATM networks have serious deficiencies with respect to at least one of these objectives.
In the prior art, many different approaches to the bandwidth management problem have been proposed and studied by various groups. Three representative approaches are summarized as follows.